Milk-alkali syndrome pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Pathophysiology

The name "milk-alkali syndrome" derives from when patients would take in excessive amounts of milk and antacids to control their dyspepsia, leading to overingestion of two key ingredients that lead to the disorder, excess calcium and excess base. Ingesting over two grams of elemental calcium per day produces this disorder in susceptible individuals. Gastrointestinal absorption of such a large amount of calcium leads to hypercalcemia. This inhibits parathyroid hormone secretion by the parathyroid gland and may also lead to diabetes insipidus. The body's attempt to rid itself of the excess base in the urine may cause bicarbonaturia and subsequent hypovolemia due to transport of sodium ions to accompany the bicarbonate.

Hypovolemia may increase the reabsorption of calcium and bicarbonate in the proximal convoluted tubules of the kidney. Elevated bicarbonate levels in the blood raises the pH, producing an alkalemia. In this state, excess bicarbonate eventually begins to reach the distal convoluted tubule, leading to sodium retention in the lumen, an effect similar to the action of thiazide diuretics, hence increasing lumen positivity and driving calcium through the passive calcium channels to bind intracellular calbindin. Finally, because of the decreased intracellular sodium, there is an increased driving force for the basolateral Na+/Ca++ antiporter, thus facilitating calcium reabsorption. Basically, hypovolemia is the culprit that prevents correction of the hypercalcemia.

The understanding of this mechanism led to the development of a simple yet elegant treatment for hypercalcemia. The first and most important step is intravenous infusion of normal saline to restore the intravascular volume, which reverses the calcium and bicarbonate retention in the PCT. Then a loop diuretic is used, but only after the volume replacement is complete, otherwise volume contraction would result, which would further exacerbate the hypercalcemia. The loop diuretics inhibit the Na-K-2Cl symporter and hence eliminate passive diffusion of potassium into the lumen via the ROMK channel. This effectively removes the net positive charge from the lumen, one of the main driving forces for calcium reabsorption via the paracellular pathway. In addition, loop diuretics increase the flow of luminal contents, which helps flush the calcium to the distal nephron.

Overview

The exact pathogenesis of [disease name] is not fully understood.

OR

It is thought that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].

OR

[Pathogen name] is usually transmitted via the [transmission route] route to the human host.

OR

Following transmission/ingestion, the [pathogen] uses the [entry site] to invade the [cell name] cell.

OR

[Disease or malignancy name] arises from [cell name]s, which are [cell type] cells that are normally involved in [function of cells].

OR

The progression to [disease name] usually involves the [molecular pathway].

OR

The pathophysiology of [disease/malignancy] depends on the histological subtype.

Pathophysiology

Physiology

The normal physiology of [name of process] can be understood as follows:

Pathogenesis

• The exact pathogenesis of [disease name] is not completely understood.

OR

• It is understood that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].
• [Pathogen name] is usually transmitted via the [transmission route] route to the human host.
• Following transmission/ingestion, the [pathogen] uses the [entry site] to invade the [cell name] cell.
• [Disease or malignancy name] arises from [cell name]s, which are [cell type] cells that are normally involved in [function of cells].
• The progression to [disease name] usually involves the [molecular pathway].
• The pathophysiology of [disease/malignancy] depends on the histological subtype.

Genetics

[Disease name] is transmitted in [mode of genetic transmission] pattern.

OR

Genes involved in the pathogenesis of [disease name] include:

• [Gene1]
• [Gene2]
• [Gene3]

OR

The development of [disease name] is the result of multiple genetic mutations such as:

• [Mutation 1]
• [Mutation 2]
• [Mutation 3]

Associated Conditions

Conditions associated with [disease name] include:

• [Condition 1]
• [Condition 2]
• [Condition 3]

Gross Pathology

On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].

Microscopic Pathology

On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].